1. Field of the Invention
The invention relates to radio-frequency laser module having a semiconductor laser disposed on a substrate and an electrical RF conductive path disposed on the substrate and connected to the laser. The invention also relates to an optoelectronic component which has such a radio-frequency laser module accommodated in a case, as well as to a method for producing a large number of radio-frequency laser modules on a semiconductor wafer.
Laser modules as well as optoelectronic components based on such laser modules are already known and have been described, for example, in Published, European Patent Application EP 0 660 467 A1 and U.S. Pat. No. 5,566,265. Furthermore, the Published, European Patent Application EP 0 660 467 A1 discloses a method by which a large number of optoelectronic laser modules can be produced on a common silicon wafer.
Such optoelectronic components are widely used in particular in data transmission and information technology. In order to allow as much information as possible to be transmitted per unit time, the components are normally operated in the radio-frequency band. The maximum achievable data rate for the component is in this case not only governed by the semiconductor laser used, but depends on a large number of other electrical, optical and constructional measures for the entire optoelectronic component, including the case used.
2. Summary of the Invention
It is accordingly an object of the invention to provide a radio-frequency laser module and a method for producing it, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type.
The invention is partially based on the object of providing a radio-frequency laser module with good RF characteristics. A further part of the object on which the invention is based is to provide an optoelectronic component having a case which accommodates the radio-frequency laser module according to the invention and which is specifically configured for radio-frequency applications. Furthermore, the invention has the aim of specifying a particularly economic and cost-effective method for producing such radio-frequency laser modules on a semiconductor wafer.
With the foregoing and other objects in view there is provided, in accordance with the invention, a radio-frequency laser module, including:
a substrate;
a semiconductor laser having an RF connection and disposed on the substrate; and
an electrical RF conductive path having a first end and a second end and disposed on the substrate, the first end to receive an external RF driver signal and the second end is electrically connected to the RF connection of the semiconductor laser, the electrical RF conductive path also has an RF matching resistor RA connected in series with the semiconductor laser.
Integration of the RF matching resistor RA into the RF conductive path disposed on the substrate (laser submount) results in the RF matching resistor RA being positioned in the immediate vicinity of the semiconductor laser. This ensures particularly effective and interference-free matching of the normally low-impedance semiconductor laser (typically 3 to 5 ohms) to the impedance of a driver circuit (normally 25 or 30 ohms), as a result of which the radio-frequency characteristics of the laser module are considerably improved.
If, furthermore, an electrical secondary conductive path is provided on the substrate and is connected to the RF connection of the semiconductor laser bypassing the RF matching resistor, this results in an interconnect structure which is applied on the substrate and is particularly advantageous for producing a large number of radio-frequency laser modules in a composite wafer.
The light produced by the semiconductor laser can pass through an electrical absorption modulator (EAM) in a manner known per se, and be RF-modulated by the modulator. In this case, the EAM is likewise disposed on the substrate, and in that an RF connecting pad (provided on the substrate) and a ground contact pad (provided on the substrate) on the EAM are connected via an RF conductive path which runs on the substrate and contains an RF matching resistor RA. Since the EAM is operated in the reverse direction, that is to say essentially represents a small capacitance, matching is carried out by using a matching resistor connected in parallel with the EAM. The joint configuration of the semiconductor laser and EAM on the same substrate results in a particularly compact overall configuration that is advantageous for RF applications and which, furthermore, can be manufactured easily. Since the RF matching resistor is formed within an RF conductive path which runs on the substrate, it is located in the immediate vicinity of the EAM, thus having an advantageous influence on the RF characteristics of the EAM.
If the RF laser module according to the invention is installed, attention must be paid to good RF configuring of the assembly. The features specified in the claims result in contact being made with the RF laser module inside the case in a manner that is advantageous for achieving high data rates.
RF laser modules with a bandwidth of more than 5 GHz can be achieved by RF blocking of the bias-current connection of the RF semiconductor laser by a suitable inductor (for example a coil with a ferrite core). Even with uncooled optoelectronic components, this allows data rates of at least 3 Gbit/s to be achieved.
An optical isolator provided in the beam path of the RF laser module can improve the RF characteristics of the laser module by largely suppressing the return of reflected laser light to the laser and, in this way, considerably reducing any interference feedback effects.
According to the invention, a large number of RF laser modules are produced on a joint semiconductor wafer, in particular a silicon wafer. This has, inter alia, the advantage that simple production and assembly sequences are possible owing to the good handling characteristics of the semiconductor wafer. At the same time, the interconnect pattern provided according to the invention on the semiconductor wafer allows a functional and long-term test of the RF laser modules (which is already known as such and is called xe2x80x9cburn-inxe2x80x9d) to be carried out while they are still within the composite wafer. During the xe2x80x9cburn-inxe2x80x9d process, the laser chip has a relatively high current applied to it for a predetermined time period, which may be 48 hours or more, during which the stability of major functional parameters is tested, and a characterization of the laser chip is determined. In the case of the RF laser modules according to the invention and having matching resistors RA disposed directly on the substrate, this xe2x80x9cburn-inxe2x80x9d procedure would, however, lead to thermal overloading of the matching resistors RA. The interconnect pattern according to the invention with a secondary conductive path ensures that the current flowing during the xe2x80x9cburn-inxe2x80x9d procedure does not flow through the RF matching resistors RA, but bypasses them via the secondary conductive paths. This allows the xe2x80x9cburn-inxe2x80x9d procedure to be carried out in an economic manner in the composite wafer during production of the laser modules, that is to say before the semiconductor wafer is cut up into the individual laser modules.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a radio-frequency laser module and a method for producing it, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.